Soil erosion is a phenomenon occurring in a wide variety of situations. It is accelerated by the action of wind and of rain and is especially bad in conditions of poor soil coherence. The loose surface is scoffed by the wind and seeds of plants that might otherwise germinate to provide a root system to hold the soil in place are disturbed. In like fashion streams of water formed in rain storms on less pervious soils carry away the surface.
In the making of cuttings, enbankments, or culverts during highway construction, large areas of steeply sloping bare soil are exposed to the weather. The construction engineer has commonly distributed a layer of straw over the surface. However, that is susceptible to loss by wind. More recently asphalt emulsions have been applied to the straw layer to hold the stalks in place. Those emulsions are undesirable because of application difficulties such as a need for heat source, plugging of the application equipment and creating a major clean-up problem.
The straw serves another function as an insulator to protect newly emerging grasses from frost when the seeding is done in the spring or late fall. Also, straw is available in the near vicinity of where needed.
Wood fibers are also used commercially to control soil erosion. They are hydraulically and directly applied onto soil from a complete "seeding slurry" or "hydromulch", which contains seeds, fertilizer and occasionally lime, in addition to wood fiber. The resulting protective mat containing seed and fertilizer is said to be sufficiently durable to withstand wind and rain exposure. In general practice however, this is not the case, since polymeric binders are almost always used to assure durable weatherability.
At a typical recommended rate of 1000-1500 lb. wood fiber per acre, 50 gal. of polymeric binder per acre and an overall applied rate of 2500 gal./acre, binder concentrations are generally less than about 1.5% based on water. These high dilutions are necessary for controlled distribution of such large quantities of wood fiber onto soil surfaces. Because of such low binder solids concentrations in the water phase, it is important to transfer them as completely as possible, into the fiber network for maximum efficiency. Failure to accomplish this results in significant loss of binder solids to the soil, thereby producing a low strength protective mat.